Rotary kilns with planetary coolers

ABSTRACT

Rotary kiln having planetary-cooling tubes is insulated in a special way and the tubes are provided with lifters which produce curtains of falling material and thus increase the heat carried into the kiln in the secondary air. This heat exchange is so effective that the heat lost in the material that leaves the tubes is compensated for by the increase in heat carried into the kiln in the secondary air.

I United States Patent 1111 ,4

[72] lnventor Flemming Edvin Jensen [56] References Cited Cop n g Denmark UNlTED STATES PATENTS 5i 1 g 122 1 1,885,845 11/1932 Lindhard 263/32 2,84 ,259 4s Patented Jan. 19, 1971 5 7/1958 Hennchse 263/32 [73] Assignee F. L. Smidth & Co.

New York, N Y, Primary ExaminerJohn J. C amby a corporation of Delaware Attorney-Pennie, Edmonds, Morton, Taylor and Adams [32] Priority Jan. 22, 1968 [33] Great Britain 3289/68 [54] g KILNS T PLANETARY COOLERS ABSTRACT: Rotary kiln having planetary-cooling tubes is in- 6 Drawmg sulated in a special way and the tubes are provided with lifters [52] U.S.Cl 263/32, hi p duce curtai o falling mater al and thus increase 34/186 the heat carried into the kiln in the secondary air. This heat [51] Int. Cl F27b 7/20 exchange is so effective that the heat lost in the material that [50] Field of Search 263/32, leaves the tubes is compensated for by the increase in heat carried into the kiln in the secondary air,

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' INVENTOR FLEMMING EDVIN JENSEN HIS ATTORNEYS PATENTEUJANIQISH 3556;495

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INVENTOR FLEMMING Eovm JENSEN S ATTORNEYS ROTARY KILNS WITH PLANETARY COOLERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to that kind of rotary kiln which has a number of cylindrical-cooler tubes mounted in planetary fashion around the outlet end of the kiln with their axes parallel or substantially parallel to the axis of the kiln, the inlet end of each cooler tube being connected to an outlet of the rotary kiln by a supply chute. The cooler tubes are usually arranged symmetrically around the discharge end of the kiln and may extend from their inlets in a direction either upwards along the kiln or downwards away from the inlet end of the kiln.

2. Description of the Prior Art The assembly of these tubes is commonly called a planetary cooler and is a well-known construction widely used in the ceramic industry, particularly for cooling cement clinker formed by burning in the rotary kiln.

The hot material leaving the rotary kiln through the com municating chutes is cooled in the cooler tubes by air which passes through the tubes in countercurrent to the stream of hot material. In the cooler the air takes up heat and is subsequently utilized in the kiln as secondary combustion air.

In the past it has been considered important to cool the material to the lowest possible temperature and hitherto the surfaces of the cooler tubes have contributed to the cooling by radiating heat to the surrounding atmosphere. To increase this radiation the cooler tubes and the chutes connecting them with the kiln outlet openings are frequently provided with fins or ribs to increase the area of the radiating surface. The heat thus radiated to the surroundings is lost. As it has hitherto been considered imperative to cool down the burnt or sintered material as much as possible, this loss has generally been accepted.

Now it is important that the amount of preheated air supplied to the kiln through the cooler should be correlated with the total amount of combustion air actually needed and that there is adequate contact between the air and the hot material, as otherwise the efficiency of the cooler will be low. If lifters, which may advantageously be helical conveyor flights as shown in my prior application Ser.'No. 757,925, filed Sept. 6, I968, are provided to lift the material in each cooler tube and discharge it in the form of falling curtains of material, the cooling air will have to pass through these curtains'before entering the kiln, and consequently the heat exchange is improved.

SUMMARY OF TI'IE INVENTION According to the invention each cooler tube of a planetary cooler has lifters which produce curtains of falling material and is thermally insulated to reduce the loss of heat by radiation. As a result, the temperature of the spent-cooling air and of the cooled material will rise. However, the heat-exchange between the material and the cooling air is so good because of the passage of the air through the curtains that the overall thermal economy is improved, that is to say the heat lost in the material that leaves the tubes is more than compensated for by the increase in the heat carried into the kiln in the secondary air combustion.

Over a length of each cooler tube extending from the inlet end the temperature is so high that high-quality heat-resistant insulating material has to be provided. This length is preferably insulated by a layer of insulating material inserted between the inner wall of the cooler tube and wearing plates which form the wall of the tube in contact with the hot material, because the amount of expensive insulation material can then be kept low. At the same time the insulating material is very well protected against damage, particularly if the wearing plates are recessed on their outer faces to receive it. Over the remaining length ordinary insulating material surrounding the tube is generally sufficient.

The wearing plates may be bolted to the tube wall and to minimize heat transmission from them to the tube wall and subsequent heat radiation to the surroundings. each wearing plate may advantageously have small supporting ribs on its outer face, only these ribs making direct contact with the tube wall.

The preferred lifters are trough-shaped helical flights, and they may advantageously be composed of sections, each section being carried by a wearing plate.

BRIEF DESCRIPTION OF Tl-IEDRAWINGS The preferred construction according -to the invention will now be described with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a vertical section through the outlet end of the kiln;

FIG. 2 is a section on the line 2-2 in FIG. 1;

FIG. 3 is a vertical section on a larger scale through a cooler tube and the corresponding outlet opening of the kiln;

FIG. 4 is a top view of sections of which a conveyor flight is composed;

FIG. 5 is a section on the line 5-5 of FIG. 4; and

FIG. 6 is a top view of a section with reinforcements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings show a rotary kiln I with a refractory lining 3 for the burning of a charge 2 (FIG. 2) of material, for instance cement raw material to clinker. v 1

Near its lower end the kiln has a number of outlet openings 4 communicating through chutes 5 with a corresponding number of cooler tubes 6 mounted with their axes parallel to the axis of the kiln and arranged equidistantly around the end of the kiln in a planetary fashion. Each chute has a heatand wear-resistant ceramic lining 7 and the inlet end of each cooler tube is also provided with such a lining 8. Over the main length each tube is lined by rectangular wearing plates 14 (FIG. 5). 1

Each cooler tube has helical trough-shaped conveyor flights 9 throughout substantially its whole length. Each cooler tube is thermally insulated by a layer of ordinary insulating material ll outside the tube wall in the relatively cool part of the tube, which may be mechanically protected and held in place in any conventional way, and by another layer of insulation 12 on the inside of the tube wall in the hot part of the tube, i.e. at the material-inlet end. This layer 12 is not continuous, but rather consists of mats 16 (FIG. 5) housed in recesses on the outer faces of the wearing plates 14.

The conveyor flights 9 are composed of sections 13 (FIGS. 4 and 5) each carried by a wearing plate 14, and the wearing plates 14 are of such dimensions that if each carries one section 13 a suitable number of conveyor flights is provided. Each section 13 is trough-shaped and inclined to the sides of the plate 14 that carries it. By making the conveyor flights of substantially identical sections carried by wearing plates they can be mounted more readily and the exchange of worn out parts does not necessitate a complete exchange of the flight. At the same time the manufacture of the parts is simpler than the manufacture of a one-piece conveyor flight. It is not necessary for all the wearing plates 14 to carry sections 13. The linings may for example include helical rows of plain plates between rows carrying flight sections.

The wearing plates are bolted to the cooler tube by means of bolts 17. The heads of the bolts are housed in recesses 15 and located under the flight section 13 so as to be protected against impact and wear by the material discharged from other conveyor flights. On the outer faces of the plates 14 there are small ribs 18 which form the recesses for the insulation mats l6. Ribs 18 extend outwardly beyond the edges of the recesses and thus make the only direct metallic contact between the wearing plate and the cooler tube. Advantageously bolts 17 may be isolated from the wearing plates by lining the bolt holes and by inserting insulating washers under the bolt heads and nuts.

The sections 13 may be stiffened by external stays 19 or internal ribs 20, or by both as shown in FIG. 5, The ribs 20 do not interfere with the conveying function of the flights, as the material while in the trough-shaped flights does not and should not to any appreciable extent move in the longitudinal direction. In addition to improving the rigidity of the flights the ribs 20 prevent the cooling air from passing along the conveyor flights.

The conveyor flights lift the material and in the course of rotation discharge it again in the form of curtains which are inclined to the axis of the kiln. As shown in FIG. 3 at the airinlet end of each tube a ring of scoops M) is provided. These scoops have sidewalls and constitute a series of buckets, which pickup material from the bottom of the tube and carry it upwards until the kiln, and therefore the tube, reaches such an angular position in the course of rotation that the material begins to fall out of the scoops 10 to form a curtain extending over approximately half the cross-sectional area of the tube, and prevents the air from passing uninterruptedly into the tube along comparatively long channels.

I claim:

1. A rotary kiln having a number of cylindrical-cooler tubes mounted in planetary fashion around its outlet end with their axes parallel or substantially parallel to the kiln axis, the inlet end of each cooler tube being connected to an outlet of the rotary kiln by a supply chute, in which lifters which produce curtains of falling material when the kiln is in use are provided in each cooler tube, the improvement wherein each cooler tube is lined with wearing plates, some of which are provided with lifters, the wearing plates being spaced inwardly from the inner surface of the tube, removably secured thereto and thermally insulated from the tube to reduce loss of heat by radiation.

2. A rotary kiln according to claim 1 in which a lengthwise portion of each cooler tube extending from the inlet end is internally insulated by a layer of insulating material disposed between the wearing plates and the inner wall of the cooler tube.

3. A rotary kiln according to claim 2-inwhich only the portion extending from the inlet end is internally insulated, and the remaining length of the tube is insulated by external insulating material.

4. A rotary kiln according to claim 3 inwhich the wearing plates, beneath which there is insulating material, are recessed to receive it.

5. A rotary kiln according to claim 4 in which the wearing plates that have recesses are bolted to the cooler tube wall and have small supporting ribs.,on their outer faces, only those ribs making direct contact with the tube wall.

6. A rotary kiln according to claim 1 in which the lifters are trough-shaped helical conveyor flights composed of sections, each section being mounted on a wearing plate.

7. A rotary kiln according to claim 6 in which the conveyor flights are stiffened by external stays or internal transverse ribs or both.

8. A rotary kiln according to claim 6 having in addition a ring of scoops at the air-inlet end of each tube to produce a transverse curtain of material over that side of the tube in which conveyor flights are moving upwards and thus to impede the entry of the incoming air into some of the channels formed between adjacent curtains. 

1. A rotary kiln having a number of cylindrical-cooler tubes mounted in planetary fashion around its outlet end with their axes parallel or substantially parallel to the kiln axis, the inlet end of each cooler tube being connected to an outlet of the rotary kiln by a supply chute, in which lifters which produce curtains of falling material when the kiln is in use are provided in each cooler tube, the improvement wherein each cooler tube is lined with wearing plates, some of which are provided with lifters, the wearing plates being spaced inwardly from the inner surface of the tube, removably secured thereto and thermally insulated from the tube to reduce loss of heat by radiation.
 2. A rotary kiln according to claim 1 in which a lengthwise portion of each cooler tube extending from the inlet end is internally insulated by a layer of insulating material disposed between the wearing plates and the inner wall of the cooler tube.
 3. A rotary kiln according to claim 2 in which only the portion extending from the inlet end is internally insulated, and the remaining length of the tube is insulated by external insulating material.
 4. A rotary kiln according to claim 3 in which the wearing plates, beneath which there is insulating material, are recessed to receive it.
 5. A rotary kiln according to claim 4 in which the wearing plates that have recesses are bolted to the cooler tube wall and have small supporting ribs on their outer faces, only those ribs making direct contact with the tube wall.
 6. A rotary kiln according to claim 1 in which the lifters are trough-shaped helical conveyor flights composed of sections, each section being mounted on a wearing plate.
 7. A rotary kiln according to claim 6 in which the conveyor flights are stiffened by external stays or internal transverse ribs or both.
 8. A rotary kiln according to claim 6 having in addition a ring of scoops at the air-inlet end of each tube to produce a transverse curtain of material over that side of the tube in which conveyor flights are moving upwards and thus To impede the entry of the incoming air into some of the channels formed between adjacent curtains. 